It is hard to name a general election in modern times in which the campaign has not boiled down to two arguments: “Time for a change” from the opposition and “Don’t take the risk” from the Government.  And when these two cases clash, the latter usually wins, as the outcomes help to prove.  The British people have plumped for giving the Opposition a workable majority only twice in the 19 national polls that have taken place since 1945 – in the sea-changing elections of 1979 and 1997, which set up Margaret Thatcher and Tony Blair for three terms in government each.

No wonder that, for Lynton Crosby, the last election was all about security.  He believed that the country would not swap the security of David Cameron for the risk of Ed Miliband, and built the successful Conservative election round that conviction.  Furthermore, the two referendums which took place during the last Parliament saw much the same pattern: in both, voters decided that it wasn’t time to change either our electoral system or Scotland’s place in the United Kingdom.  Over 40 years ago, they took the same view of Britain’s membership of the Common Market, voting to remain by 67 per cent to 33 per cent.

All this helps to explain why Lord Ashcroft, in his article this morning on this site about his new polling research, zeroes in on the central role of risk in its successor, the referendum on Britain’s EU membership that may take place as early as this summer.  “For many many people,” he writes, “the question will come down to the balance of risk.”

Many cases will be made by people during the long campaign leading up to that poll – and, indeed, are being made now.  ConservativeHome is for Brexit, and identifies five main benefits: fewer politicians, better immigration control, more money for public services and tax cuts, a stronger economy and global engagement.  VoteLeave stresses control.  “Vote Leave, take control”, it declares.  Leave EU declares that “Together, we can win back our country”.  Our columnist Daniel Hannan says at the top of his website that the EU “is making its member countries “poorer, less democratic and less free”.

These points are all to the point, but none of them will be decisive – and nor, for that matter, will those being put by supporters of Remain.  This is because argument is pitched to the mind, and what ultimately matters in polls is less the mind than the heart – or, if you like, the gut.  Human beings are not calculating machines and, for this reason, politics cannot be a merely rational exercise.  And the history of British polls and referendums suggests that fear, that inhibitor of risk and friend of the status quo, is more electorally potent than anger, that driver of risk and ally of change.

The success or failure of the Leave campaign will thus hang on turning the conventional wisdom on its head – and persuading voters that staying in the EU is a bigger risk than leaving: to our prosperity, to our security, to our jobs, living standards and families’ future. This will be a tough sell, though far from an impossible one.